Doom 3/Doom3 Doomguy is not the same as OG Doomguy because he does not share the same qualities as OG.
OG Doomguy:
Can sprint for all eternity practically
High endurance
High strength
Fights on the Martian moons, Phobos and Deimos, and on Earth, as well as in Hell
Doom 3/Doom3 Doomguy:
Can sprint for short bursts of time
Somewhat high endurance
Somewhat high strength
Fights on Mars and in Hell

Since Doom 5 is probably going to be a remake of Doom II, and we have already seen the Icon of Sin (dormant) in Doom '16, so who or what would the final boss for the next one be?
I was kind of thinking about maybe Satan, since it is Hell and Satan is the Lord of Hell, so it would make sense right?
Tell me what you guys think.